In a co-axial straight cable, the central conductor and the outer conductor carry equal currents in opposite directions. The magnetic field is zero:
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Question

In a co-axial straight cable, the central conductor and the outer conductor carry equal currents in opposite directions. The magnetic field is zero:

G1 Physics · Accepted Answer

Outside the coaxial cable, the net enclosed current is: I(enclosed) = I - I = 0 Using Ampere's law: ∮ B→ · dl→ = μ₀I(enclosed) Therefore: B = 0 Hence, the magnetic field is zero outside the cable.